| Summary: | A significant sea surface temperature increase has been reported for the Southwestern Atlantic Ocean between 20° S-50° S over the last decades. Zooplankton organisms are highly sensitive to temperature rise. They play a very important role in marine ecosystems by providing the main pathway of energy transfer from primary producers to consumers. Seasonal and interannual (2000-2017) variability of metazooplankton in relation to environmental changes, particularly temperature, were analyzed at the EPEA station (38° 28′ S-57° 41′ W). Copepods, appendicularians, cladocerans, chaetognaths, and lamellibranch larvae were identified and quantified. Temperature exhibited a positive interannual trend during the series, whereas the Simpson parameter showed a decreasing tendency and salinity remained almost constant. Adults, copepodites, and nauplii of small copepods belonging to Oithonidae (mostly Oithona nana) and Paracalanidae-Clausocalanidae families dominated the metazooplankton community during the study period. Three groups of taxa with different seasonal patterns of variability were clearly identified. Members of Oithonidae exhibited positive interannual trends, whereas lamellibranch larvae and Calanidae showed negative interannual trends. A direct influence of temperature anomaly on these changes is suggested as well as possible indirect effects of this anomaly upon zooplankton through different phytoplankton fractions. Under the current scenario of climate change, the maintenance of this time-series becomes crucial in order to evaluate the eventual transfer of the environmental variability to the local food webs through planktonic organisms.
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